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Electron-microscopic studies on developing intramural ganglia of the small intestine in human and rabbit fetuses
Insights
Synapse development in the developing gut correlates with the emergence of intestinal peristalsis. Electron microscopy reveals distinct synapse types appearing as gut muscle layers and motility mature in human and rabbit fetuses.
Area of Science:
- Neuroscience
- Developmental Biology
- Gastroenterology
Background:
- Intestinal peristalsis is crucial for nutrient absorption and waste elimination.
- The development of the enteric nervous system, including Auerbach's plexus, parallels gut motility.
- Understanding synapse formation is key to comprehending the maturation of gut function.
Purpose of the Study:
- To investigate the ultrastructural appearance of synapses in Auerbach's ganglion.
- To correlate synapse development with the onset and progression of intestinal peristalsis.
- To characterize different types of nerve terminals during fetal development.
Main Methods:
- Electron microscopy was used to examine synapses in the intramural ganglion (Auerbach's plexus).
- Studies were conducted on human and rabbit fetuses from 12 days post-conception to birth.
- Findings were correlated with observed stages of intestinal muscle layer development and peristalsis.
Main Results:
- Primitive synapses with clear and cored vesicles were observed in early stages (Stage I) before muscle layer development.
- As the circular muscle layer developed (Stage II), three types of synapses emerged, with specific vesicle characteristics and membrane specializations.
- Further synapse types (IV-V) containing cored vesicles appeared with longitudinal muscle development (Stage III), and a distinct type (VI) with large-cored vesicles was noted when antiperistalsis ceased (Stage IV).
Conclusions:
- Synapse maturation in Auerbach's ganglion is a dynamic process closely linked to the development of intestinal motility.
- Distinct morphological types of nerve terminals likely represent different neurotransmitter systems or functional roles.
- These findings provide insights into the neurobiological basis of gut development and function.
Abstract:
Electron-microscopic studies were made on the appearance of synapses in the intramural ganglion (Auerbach) and findings were correlated with the onset and development of intestinal peristalsis in 6- to 30-week-old human and rabbit fetuses from the 12th day after conception until birth. At stage I, in which the small intestine shows no indication of a muscle layer or spontaneous peristalsis, primitive synapses containing several clear vesicles and a few cored vesicles are seen on neuroblasts and their processes (dendrites). At stage II, in which the circular muscle is developed and bidirectional peristalsis occurs, synaptic profiles can be classified into 3 types. Type 1 is the most numerous but seldom shows membrane specificity on the synaptic portion. Types 2 and 3 have small flattened vesicles and small round vesicles, respectively. They are further characterized by thickening of snyaptic membranes and aggregation of small clear vesicles associated with the presynaptic membrane. At stage III, the longitudinal muscle layer develops in the small intestine. At this stage, nerve terminals containing mainly cored vesicles have been observed and classified into types 4 and 5, according to their morphology. At stage IV, antiperistalsis no longer occurs and type 6 nerve terminals in the intramural ganglia can be recognized by their densely packed, large-cored vesicles. The possible physiological significance of the nerve terminals has been discussed.